An increase in crop intensity could improve crop yield but may also lead to a series of environmental problems, such as depletion of ground water and increased soil salinity. The generation of high resolution(30 m) cr...An increase in crop intensity could improve crop yield but may also lead to a series of environmental problems, such as depletion of ground water and increased soil salinity. The generation of high resolution(30 m) crop intensity maps is an important method used to monitor these changes, but this is challenging because the temporal resolution of the 30-m image time series is low due to the long satellite revisit period and high cloud coverage. The recently launched Sentinel-2 satellite could provide optical images at 10–60 m resolution and thus improve the temporal resolution of the 30-m image time series. This study used harmonized Landsat Sentinel-2(HLS) data to identify crop intensity. The sixth polynomial function was used to fit the normalized difference vegetation index(NDVI) and enhanced vegetation index(EVI) curves. Then, 15-day NDVI and EVI time series were then generated from the fitted curves and used to generate the extent of croplands. Lastly, the first derivative of the fitted VI curves were used to calculate the VI peaks;spurious peaks were removed using artificially defined thresholds and crop intensity was generated by counting the number of remaining VI peaks. The proposed methods were tested in four study regions, with results showing that 15-day time series generated from the fitted curves could accurately identify cropland extent. Overall accuracy of cropland identification was higher than 95%. In addition, both the harmonized NDVI and EVI time series identified crop intensity accurately as the overall accuracies, producer’s accuracies and user’s accuracies of non-cropland, single crop cycle and double crop cycle were higher than 85%. NDVI outperformed EVI as identifying double crop cycle fields more accurately.展开更多
The purpose of this study was to compare the dose distribution of intensity-modulated ra- diotherapy （IMRT） in 7 and 5 fields as well as 3-D conformal radiotherapy （3D-CRT） plans for gastric cancer using dosimetri...The purpose of this study was to compare the dose distribution of intensity-modulated ra- diotherapy （IMRT） in 7 and 5 fields as well as 3-D conformal radiotherapy （3D-CRT） plans for gastric cancer using dosimetric analysis. In 15 patients with gastric cancer after D1 resection, dosimetric pa- rameters for IMRT （7 and 5 fields） and 3D-CRT were calculated with a total dose of 45 Gy （1.8 Gy/day） These parameters included the conformal index （CI）, homogeneity index （HI）, maximum dose spot for the planned target volume （PTV）, dose-volume histogram （DVH） and dose distribution in the organs at risk （OAR）, mean dose （Dmean）, maximal dose （Dmax） in the spinal cord, percentage of the normal liver volume receiving more than 30 Gy （V30） and percentage of the normal kidney volume receiving more than 20 Gy （V20）. IMRT （7 and 5 fields） and 3D-CRT achieved the PTV coverage. However, IMRT presented significantly higher CI and HI values and lower maximum dose spot distribution than 3D-CRT （P=0.001）. For dose distribution of OAR, IMRT had a significantly lower Dmean and Dmax in spinal cord than 3D-CRT （P=-0.009）. There was no obvious difference in V30 of liver and V20 of kidney between IMRT and 3D-CRT, but 5-field IMRT showed lower Dmean in the normal liver than other two plans （P=0.001）. IMRT revealed favorable tumor coverage as compared to 3D-CRT and IMRT plans. Specifically, 5-field IMRT plan was superior to 3D-CRT in protecting the spinal cord and liver, but this superiority was not observed in the kidney. Further studies are needed to compare differences among the three approaches.展开更多
基金supported by the China Postdoctoral Science Foundation (2017M620075 and BX201700286)the National Natural Science Foundation of China (NSFC-61661136006)
文摘An increase in crop intensity could improve crop yield but may also lead to a series of environmental problems, such as depletion of ground water and increased soil salinity. The generation of high resolution(30 m) crop intensity maps is an important method used to monitor these changes, but this is challenging because the temporal resolution of the 30-m image time series is low due to the long satellite revisit period and high cloud coverage. The recently launched Sentinel-2 satellite could provide optical images at 10–60 m resolution and thus improve the temporal resolution of the 30-m image time series. This study used harmonized Landsat Sentinel-2(HLS) data to identify crop intensity. The sixth polynomial function was used to fit the normalized difference vegetation index(NDVI) and enhanced vegetation index(EVI) curves. Then, 15-day NDVI and EVI time series were then generated from the fitted curves and used to generate the extent of croplands. Lastly, the first derivative of the fitted VI curves were used to calculate the VI peaks;spurious peaks were removed using artificially defined thresholds and crop intensity was generated by counting the number of remaining VI peaks. The proposed methods were tested in four study regions, with results showing that 15-day time series generated from the fitted curves could accurately identify cropland extent. Overall accuracy of cropland identification was higher than 95%. In addition, both the harmonized NDVI and EVI time series identified crop intensity accurately as the overall accuracies, producer’s accuracies and user’s accuracies of non-cropland, single crop cycle and double crop cycle were higher than 85%. NDVI outperformed EVI as identifying double crop cycle fields more accurately.
文摘The purpose of this study was to compare the dose distribution of intensity-modulated ra- diotherapy （IMRT） in 7 and 5 fields as well as 3-D conformal radiotherapy （3D-CRT） plans for gastric cancer using dosimetric analysis. In 15 patients with gastric cancer after D1 resection, dosimetric pa- rameters for IMRT （7 and 5 fields） and 3D-CRT were calculated with a total dose of 45 Gy （1.8 Gy/day） These parameters included the conformal index （CI）, homogeneity index （HI）, maximum dose spot for the planned target volume （PTV）, dose-volume histogram （DVH） and dose distribution in the organs at risk （OAR）, mean dose （Dmean）, maximal dose （Dmax） in the spinal cord, percentage of the normal liver volume receiving more than 30 Gy （V30） and percentage of the normal kidney volume receiving more than 20 Gy （V20）. IMRT （7 and 5 fields） and 3D-CRT achieved the PTV coverage. However, IMRT presented significantly higher CI and HI values and lower maximum dose spot distribution than 3D-CRT （P=0.001）. For dose distribution of OAR, IMRT had a significantly lower Dmean and Dmax in spinal cord than 3D-CRT （P=-0.009）. There was no obvious difference in V30 of liver and V20 of kidney between IMRT and 3D-CRT, but 5-field IMRT showed lower Dmean in the normal liver than other two plans （P=0.001）. IMRT revealed favorable tumor coverage as compared to 3D-CRT and IMRT plans. Specifically, 5-field IMRT plan was superior to 3D-CRT in protecting the spinal cord and liver, but this superiority was not observed in the kidney. Further studies are needed to compare differences among the three approaches.
